1. Field of the Invention
The present invention relates generally to radiation detection systems, and more particularly, to a system for monitoring radon-222 exposure within a number of different sample environments under a variety of conditions.
2. Discussion of the Prior Art
The uranium mining industry has long known that radon-222 gas will collect in various concentration levels at or near the surface of the earth above naturally occurring uranium 238 deposits. Accordingly, a large number of radiation detectors have been developed over the last decade to measure the concentration of radon-222 gas in the atmosphere above the earth or in the ground just below the earth's surface.
Radon-222 is a radioactive gas with a half-life of 3.825 days and is generated during the radioactive transformation of uranium 238. During the initial decay of radon-222 to polonium-218, radon atoms will emit alpha particles having approximate voltages of 5.0 MeV (megaelectron volts). The quantity of these alpha particles is directly proportional to the level of radon concentration within the immediate environment. Thus, measuring the quantity of alpha particles within a certain area has long been an accepted method of determining the level of radon concentration, (see U.S. Pat. No. 3,665,194).
One prior art method of detecting alpha particles emitted by decaying radon-222 within a certain environment consists of positioning an alpha particle detector within a housing and selectively passing air or gas across the surface of the detector, thereby allowing the detector to interact with the alpha particles (U.S. Pat. Nos. 4,342,913 and 4,607,165). Other prior art devices use filters to capture radon-222 atoms and/or daughter isotopes from the surrounding environment so that the alpha particle emitting matter can be disposed in close proximity to the radiation detector. Related prior art devices are disclosed by U.S. Pat. Nos. 3,968,371 and 3,558,884, as well as U.S. Pat. No. 4,518,860. (See also U.S. Pat. Nos. 4,417,142; 4,426,575; and 4,468,558, all issued to Kristiansson et al, for similarly related devices).
The type of radiation detection devices which have been used in prior art devices has varied greatly. A number of these devices, such as those using a chamber inserted in the ground, have used a scintillation counter (U.S. Pat. No. 4,352,014), a nuclear track detector foil (U.S. Pat. No. 4,385,236), a phosphor screen in combination with a photo multiplier (U.S. Pat. No. 3,056,886), or a semiconductor detector (U.S. Pat. No. 4,104,523, issued August 1, 1978, to Wolfert). When charged particles move through a semiconductor of a semiconductor device they lose kinetic energy, primarily through ionization processes, just as they do when they move through the gas of a gas detector. By developing electric fields across a depletion region of an n-type/p-type semiconductor, a sensitive region can be developed. When an ionization particle traverses the sensitive region it produces electron-hole pairs that are swept away by the electric field and thereby produce an electric-current pulse which can be detected and measured. Although such devices are known, their detection accuracy has not been high and the cost of adequately sized and accurate detectors has been prohibitive.
Although prior art radon-222 detectors have proven capable of detecting levels of radon concentration above or in the ground, such devices are restricted as to the type of different environments or different conditions in which they can be used. In addition, such devices have had little utility outside of the scientific environment because the devices reported levels of radon concentration in terms which carried little or no meaning for most persons. A need has arisen for a radon-222 detector which is capable of operating in a number of different environments under a variety of different conditions and reporting the levels of radon concentration in easily understandable terms.
Events occurring in the past decade have lead to greater concerns regarding the potential environmental human health hazards presented by human produced and naturally occurring radioactive sources in the vicinity of the home and work place. The high-energy levels of alpha particles, which are much higher than the other by-products of atomic break-down, such as beta particles (electrons) and gamma radiation (photons), can cause chemical reactions to occur in virtually any object, when that object is struck by an alpha particle. In some objects the displacement of electrons may not prove to be consequential since atoms are simply displaced with no resulting change in atomic structure. In the human body, however, the displacement of a single electron or atom can cause a local chemical reaction which may eventually result in cancer formations. In view of the above, the Environmental Protection Agency has recently issued a warning concerning the cancerous effect of certain levels of radon-222 concentration in the home and work place.